Diamond abrasive tool



- N b in 1970 P. BLACKMER ETAL 3,540,162

DIAMOND ABRASIVE TOOL Filed Feb. 23, 1967 I NVENTORS. W LACK/WEE United States Patent O 3,540,162 DIAMOND ABRASIVE TOOL Paul W. Blackmer and Gunnar E. Hollstrom, Worcester, Mass., assignors to Norton Company, Worcester, Mass., a corporation of Massachusetts Filed Feb. 23, 1967, Ser. No. 618,104 Int. Cl. B24d /00 US. Cl. 51-206 5 Claims ABSTRACT OF THE DISCLOSURE A bonded abrasive tool comprising:

(a) a plurality of diamond abrasive grains having a given grain size;

(b) an inert filler material separating the diamond grains and having approximately the same given grain size; and

(c) a metal bond of diecast metal filling the voids between and bonding the diamond abrasive grains and the inert filler material.

BACKGROUND OF THE INVENTION The field of the invention is abrasive tools made With silicon carbide, diamonds and metal oxide grits and the processes of making such tools. The invention particularly relates to a diamond abrasive tool having an inert filler and a matrix of metal bonding material.

The prior art uses, raw materials, standards and methods of making bonded diamond abrasive products are disclosed in Kirk-Othmer, Encyclopedia of Chemical Technology, second edition, vol. 1, particularly pages 25, 28, 31-33, 37 and 38, and vol. 4, particularly pages 293 and 301.

Both natural and synthetic diamonds are useful in the manufacture of bonded diamond abrasive products and the usual products find their greatest application as bonded diamond segments mounted on centers or hubs to form diamond grinding wheels or saws. Diamond wheels are available in diamond grain sizes ranging from 16 to 2000 mesh with 46 to 400 mesh being the preferred range. The grain or grit sizes available are determined, according to the US. Standard Sieve Series. These diamond wheels are commercially available in standard concentrations of 25, 50, 75 and 100, where 100 concentration corresponds to 25% diamonds by volume and 50 concentration corresponds to 12.5% diamonds by volume, etc.

In a particular application of bonded diamond abrasive Wheels, the face of the wheel is contoured during manufacture to conform to a shape to be generated in a workpiece. Such a prior art process is disclosed in US. Pat. 3,288,580, of Frantisek Curn. The grinding wheel produced by the process of Curn, however, has a specific utility in precision grinding activities and it contains only a single layer of diamonds. When this layer is worn down, however, the grinding wheel is no longer useful.

SUMMARY OF THE INVENTION Having in mind the limitations of the prior art, it is an object of the present invention to provide a bonded diamond abrasive product having a deeper layer of diamonds.

Another object of the present invention is a diamond abrasive product having a contoured grinding face.

Still another object of the present invention is a bonded diamond abrasive tool having an inert filler of the same particle size as the diamonds separating the layers of diamonds and a bonding matrix of diecast metal.

Upon further study of the specification and claims, other objects and advantages of the present invention will become apparent.

The improved bonded abrasive tool of the present invention is molded to form a grinding wheel by first machining an outer mold ring from an aluminum alloy. A second part which becomes the center of the wheel is spaced inwardly from this ring and is disposed concentric with it to define an annular space. If it is desired to have a contoured surface on the outside diameter of the finished grinding wheel, the shape of the surface desired is machined into the inside diameter of the mold ring. A center portion, which later becomes the grinding wheel hub, is also machined to have such a contour and may be in the form of an aluminum alloy wheel disposed concentrically within the mold ring. For standard straight faced grinding wheels, the mold for forming the grinding face of the diamond section and the surface of the mold center are substantially straight.

With the smaller mold center disposed concentrically within the mold ring an annular space of known volume is formed, which ultimately is filled to become the diamond containing section of the finished wheel. The weight of diamond grains desired for a particular diamond concentration is calculated for the given volume. The weight of aluminum alloy particles and antimony particles needed to fill the remaining volume of the space of the diamond section is also calculated. The aluminum alloy is preferably used in a volume ratio of two parts aluminum to one part antimony. The aluminum alloy and antimony particles are screened to the same grit size as the diamond grains selected, the proper portions of diamond grains, aluminum alloy and antimony are then measured and are mixed by tumbling, the mixture being poured into the space between the mold center and the mold ring.

The aluminum alloy and antimony fillers having the same particle size as the diamonds, maintain the diamonds evenly distributed in the annular space between the mold center and ring. With the diamond grains suspended in this way, the mold is placed in a diecasting apparatus and a molten diecasting metal is flowed into the annular diamond section to fill the voids between the diamond grains and the inert fillers.

The mold ring is then removed from the outside surface of the grinding wheel and the center portion of the mold center is machined or bored to conform to the dimensions of the usual mounting hub of a grinding machine. The diamond grinding wheel is then ready for final finishing to condition the surface of the grinding wheel for use before testing, inspection and shipment.

BRIEF DESCRIPTION OF THE DRAWING The description of the present invention is aided by reference to the annexed figures wherein:

FIG. 1 shows an enlarged cross section of the diamond section of a grinding wheel and shows the surface of contact of the abrasive carrying section with its center;

FIG. 2 is a fragmentary cross sectional view of the mold ring for the wheel shown in FIG. 1;

FIG. 3 is a fragmentary cross sectional view of the mold ring assembled with the mold center and the abrasive grains and inert filler distributed therebetween; and

FIG. 4 shows the finished wheel in cross section.

With particular reference to FIG. 1, the abrasive containing section 2 is shown attached to wheel hub 1. The abrasive section has a contoured grinding surface 3 and the hub 1 has a knurled and contoured surface 4. The abrasive grits which are preferably diamonds 5 are supported by a bond material 6 having inert filler particles 13 therein.

The outer mold ring 7 is shown in FIG. 2 as having a locating bore 8, a mold cavity 9 and a contoured surface 10. A method for making the mold, assembling it with the center, and completing the die casting step are all described in the Corn Pat. 3,288,580. In FIG. 3, the mold center 11 with its locating pin portion 12 is shown inserted in and assembled with the outer mold ring. The abrasive grits and inert filler particles 13 are shown distributed between the mold center and the mold ring.

The finished grinding wheel of FIG. 1 is shown in FIG. 4 on a smaller scale, with the center mounting hole 14 bored through the hub 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The outer mold ring of the present invention is preferably machined from an inexpensive wrought aluminum alloy containing copper and magnesium as primary alloying elements, together with minor amounts of iron, nickel and titanium. A cutting tool of high speed steel having a rake angle of 3 on the side and from 15 to on the face may be employed for shaping the critical contour of the wall 10 on a toolmakers lathe.

The mold center is preferably made of the same material as the mold ring but it is suggested that in some instances standard diamond wheel center compositions may be used.

The abrasive grits used may be either silicon carbide, alumina, or other known abrasive material, but preferably diamonds are used in the present invention which may be from natural or synthetic sources with a particle size from about 80 to 200 grit preferred, wherein 100 grit size is particularly preferred. In addition to the standard diamond concentrations of 25, 50, 75 and 100, the diamond tools of the present invention are particularly useful in diamond concentrations up to 200 i.e., 50% diamonds by volume. It is suggested that this invention is useful, however, in the range of concentrations up to 300 or 75% diamonds by volume.

The inert filling material of the diamond section is preferably a mixture of chips formed by comminuting and screening chips produced by machining the mold ring, these chips being mixed with antimony powder. The volume ratio of aluminum alloy powder to antimony is preferably two to one. The inert fillers are screened to the corresponding grit size of the diamonds used so that the diamonds may be uniformly distributed throughout the mix and do not settle out from a loosely packed mixture.

The diecasting alloy preferred for use as a binder for the diamond section preferably comprises 65 percent of a conventional zinc diecasting alloy containing copper and aluminum as the principal alloying elements, about 32 percent cadmium and about 3 percent commercial silver solder. It is the intention of the present invention to provide a binding alloy with a melting point lower than the melting point of the inert filling material and therefore other alloys fulfilling the required conditions may be used.

The process of molding the diamond abrasive tool of the present invention is carried out by machining the mold ring shown in FIG. 2. The mold center 11 is then prepared to preferably have a correspondingly contoured periphery and is inserted in the mold ring. The mixture of diamonds 6 and inert materials 13 all having approxi- 'mately the same particle size are then poured into the cavity formed between the center 11 and the mold 7. This space or cavity may conveniently be designed to be /8" wide in a straight faced grinding wheel and in a contoured wheel a corresponding cavity volume is defined. The mixture of diamond grains and inert particles, prepared by tumbling, may be spread or fed into the cavity by rotating the mold assembly. The loosely packed mixture of diamonds and inert materials after being evenly distributed is then bonded together and to the center by inserting the mold assembly into a diecasting apparatus and by adding a molten diecasting metal to fill the pores between the diamonds and inert fillers.

The assembly is then cooled and the outer mold is removed by machining or otherwise stripping the mold ring away. The locating pin portion 12 of the center, shown in FIG. 3, is then machined away and the center mounting hole 14 is bored into the center to form the grinding wheel of FIG. 4.

It is understood that other bonded abrasive products besides grinding wheels may be produced and are included in the concept of the invention. The preferred diamond tools produced by the present invention are characterized by long grinding life with little attention required to maintain the grinding face in true dimension. However, in use, when the contour of the wheel loses its precise shape, any suitable dressing method may be used to restore the original form and thus a longer wearing form grinding wheel is provided.

It will be understood that this invention is susceptible to modification in order to adapt it to different usages and conditions and, accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

What is claimed is:

1. A bonded abrasive tool comprising:

a driving center having a knurled contoured peripheral surface extending to adjacent side surfaces;

an abrasive containing section of substantially uniform thickness extending entirely across the contoured peripheral surface to the side surfaces and having a contoured grinding surface concentric with the contour of hte knurled peripheral surface;

a plurality of substantially evenly distributed abrasive grains in said section having a given grain size;

an inert particulate filler material in said section separating said grains and said particles having approximately said given grain size; and

a metal bond of die cast metal filling the voids between and bonding said abrasive grains and said filler material to said center.

2. The bonded abrasive tool of claim 1, wherein said abrasive grains are diamonds and said given grain size is between about and 200 grit.

3. The bonded abrasive tool of claim 2, wherein said given grain size is about grit.

4. The bonded abrasive tool of claim 1, wherein said filler material is a mixture of aluminum alloy particles and antimony particles.

5. The bonded abrasive tool of claim 1, wherein said diecast metal has a melting point lower than the melting point of said filler material.

References Cited UNITED STATES PATENTS 2,238,351 4/1941 Van Der Pyl. 2,766,565 10/ 1956 Robinson 51-206 3,069,816 12/1962 Pratt 51-206 3,288,580 11/1966 Curn 51-206 X HAROLD D. QWHITEHEAD, Primary Examiner 

